Metatarsus Adductus
1. Definition—Anatomic variation
a. Congenital adductus of the forefoot on the hindfoot through the midfoot (Figure 5-35)
b. Classification of congenital MA according to severity, using the “heel bisector method,” is not prognostic, but can be used to help document initial alignment and the change in alignment that occurs both spontaneously and with intervention (Figure 5-36).
c. Classification of congenital MA according to flexibility has been shown to have prognostic value (Figure 5-37).
2. Alternate definition—Deformity
a. Congenital adductus of the forefoot on the hindfoot through the midfoot that does not spontaneously correct (Figure 5-38)
b. Congenital adductus of the forefoot on the hindfoot through the midfoot as a residual segmental deformity of a clubfoot
c. Congenital adductus of the forefoot on the hindfoot through the midfoot as the forefoot deformity in a skewfoot
Figure 5-35. Plantar view of an infant foot with congenital MA. The lateral border of the foot is convex and the medial border is concave. There may be a vertical skin crease along the medial midfoot. The hindfoot is in neutral alignment. There is normal ankle dorsiflexion.
3. Elucidation of the segmental deformities
a. Forefoot—neutral or supinated
b. Midfoot—adducted
c. Hindfoot—neutral
d. Ankle—neutral
4. Imaging
a. None initially for congenital MA
b. Standing AP and lateral of the foot for persistent deformity when surgery is being considered in an older child (Figure 5-39)
c. There is no definitive association with hip dysplasia, so routine imaging of the hips is not indicated. A careful hip examination should be performed along with an assessment for the true risk factors for developmental dysplasia of the hip (DDH), which are a positive family history and breech presentation.
Figure 5-36. The “heel bisector method” for assessing the severity of MA assumes that, in a normal foot, the line that bisects the heel extends to the interspace between the 2nd and 3rd toes. The dashed lines represent the medial and lateral borders of the heel. The solid lines represent the heel bisectors. The heel bisector of the foot shown on the left (right foot) intersects with the 4th toe, whereas that on the right (left foot) intersects with the 3rd toe. The left foot is, therefore, less deformed.
Figure 5-37. The flexibility method for assessing MA. A. MA. B. Rigid MA—the forefoot cannot be easily passively abducted to create a straight lateral border. C. Partly flexible MA—the forefoot can be easily passively abducted to create a straight lateral border. D. Flexible MA—the forefoot can be easily passively abducted beyond a straight lateral border. Obviously, the definition of easy has not been quantified.
5. Natural history
a. Most congenital MA deformities (perhaps 90% to 95%) spontaneously correct in the first 1 to 3 years of life (see Basic Principle #4, Figure 2-2, Chapter 2).
b. For those with persistence of significant deformity, there may be pain and tenderness along the lateral midfoot and/or medial to the head of the 1st MT and the hallux.
6. Nonoperative treatment
a. None indicated—for flexible (the forefoot can be easily passively abducted beyond a straight lateral border) and partly flexible (the forefoot can be easily passively abducted to create a straight lateral border) deformities (Figure 5-37)—90% to 95% of the total
b. Serial long-leg casting for rigid (the forefoot cannot be easily passively abducted to create a straight lateral border) deformities
i. best initiated between 6 and 12 months—after persistence of deformity is confirmed and before the foot becomes too stiff
ii. cast the foot with the ankle in slight plantar flexion and the subtalar joint in slight inversion to avoid inadvertent valgus stress on the subtalar joint. Dr. Ponseti described this casting technique as well as that for clubfoot and stressed the important differences between the two methods (Figure 5-40).
Figure 5-38. Persistent MA in a toddler. A. Top view shows adductus of the forefoot on the hindfoot through the midfoot. B. Posterior view shows neutral alignment of the hindfoot and adductus of the forefoot.
Figure 5-39. A. AP x-ray of a foot in an older child with persistent MA. The MTs are normally shaped, but are mal-oriented at the tarsometatarsal joints (Lisfranc joints). B. The medial cuneiform is rectangular in shape in a normal foot (black rectangle). In a foot with MA, the medial cuneiform is trapezoid-shaped (purple line indicates distal articular surface of the bone) which creates mal-orientation of the 1st MT–medial cuneiform joint, i.e., MA. The other cuneiform bones and the cuboid are also, no doubt, trapezoid-shaped, but it is more difficult to appreciate their shapes on plane x-rays. There is mild abduction of the navicular on the head of the talus, suggesting that this foot could, in fact, be classified as a mild skewfoot. The forefoot/midfoot deformity is the same in the two conditions.
7. Operative indications
a. Failure of nonoperative treatment to relieve pain and tenderness located along the lateral midfoot and/or medial to the head of the 1st MT and the hallux, despite prolonged attempts to modify and adjust shoe wear (Figure 5-41)
8. Operative treatment with reference to the surgical techniques section of the book for each individual procedure
a. Cuboid closing wedge osteotomy (see Chapter 8) and distal abductor hallucis recession (see Chapter 7) and medial capsulotomy 1st MT/medial cuneiform joint—perform this in young children before there is adequate ossification of the medial cuneiform (under around age 4 years)
b. Medial cuneiform (medial) opening wedge osteotomy (see Chapter 8) and cuboid closing wedge osteotomy (see Chapter 8) and possible distal abductor hallucis recession (see Chapter 7)—perform thisin older children and adolescents
c. NOTE: The foot-CORA for MA (see Assessment Principle #18, Figure 3-21, Chapter 3) is the medial cuneiform on the medial column of the foot and the cuboid on the lateral column. Therefore, tarsometatarsal capsulotomies (the Heyman–Herndon procedure) and base MT osteotomies are distal to the foot-CORA for this deformity and are not indicated. Additionally, tarsometatarsal capsulotomies have been shown to lead to premature degenerative arthritis in those joints, and base MT osteotomies have been associated with 1st MT physeal injury and lesser MT malunions and nonunions.
Skewfoot
1. Definition—Deformity (some unknown percentage are Anatomic variations)
a. Congenital or acquired valgus deformity of the hindfoot with adductus deformity of the forefoot (Figure 5-42)
b. Idiopathic, iatrogenic (following clubfoot treatment), or associated with an underlying neuromuscular or chromosomal abnormality (syndromic)
2. Elucidation of the segmental deformities
a. Forefoot—pronated and plantar flexed at Lisfranc joints
b. Midfoot—adducted
c. Hindfoot
i. Valgus/everted in older children and adolescents
ii. often Neutral in the coronal plane with Abduction at the talonavicular joint in young children, but can be valgus/everted
d. Longitudinal arch
i. Normal height in most young children with idiopathic deformity
ii. Flat in many/most older children and adolescents with idiopathic and acquired deformity
iii. Normal or flat in syndromic cases
e. Ankle
i. Neutral in most young children with idiopathic deformity
ii. Plantar flexed (equinus) in many/most older children and adolescents with idiopathic and acquired deformity
iii. Neutral or plantar flexed (equinus) in syndromic cases
f. In the first decade of life,
i. Children have the obvious skew deformity in the frontal plane, i.e., adduction of the forefoot on the midfoot and abduction of the midfoot on the hindfoot.
ii. The longitudinal arch is often average or higher than average in height and there is full flexibility of the tendo-Achilles.
iii. The hindfoot does not appear to be in valgus.
iv. The AP and lateral x-rays do not seem to represent the same foot. On the basis of the lateral position of the navicular on the head of the talus seen on the AP x-ray, one would expect a flatfoot deformity both clinically and radiographically, but the lateral x-ray often looks normal (Figure 5-43).
g. In the second decade of life,
i. The frontal plane deformities persist, i.e., adduction of the forefoot on the midfoot and abduction of the midfoot on the hindfoot.
ii. But the longitudinal arch drops, the hindfoot everts to valgus, and the tendo-Achilles becomes contracted in some/all affected feet.
iii. It looks like a flatfoot.
iv. The AP x-ray looks the same as in the younger children, but the lateral x-ray shows the flatfoot appearance that one would expect to see (Figure 5-44).
Figure 5-40. A. When manipulating a foot with MA, three points of pressure are applied, as if one were straightening out a bent twig. The black arrows show the three pressure points. B. The pressure points for MA manipulation are the medial side of the head of the 1st MT, the cuboid/lateral midfoot, and the medial side of the posterior calcaneus (three black arrows). Manipulation of a clubfoot is quite different, because the primary goal is to evert, or spin, the acetabulum pedis around the talus. The distal pressure point is the same for both deformities, i.e., the medial side of the 1st MT head. Importantly, the midfoot pressure point in a clubfoot is the dorsolateral aspect of the head of the talus (blue arrow). The 1st MT is, effectively, a handle that is used to evert the acetabulum pedis around the fulcrum that is the head of the talus. In so doing, the cavus and MA deformities in a clubfoot are concurrently corrected. The posterior calcaneus must rotate away from the lateral malleolus in a clubfoot, so the posterior pressure point is the medial malleolus, not the calcaneus. (From Ponseti IV. Congenital Clubfoot: Fundamentals of Treatment. Oxford: Oxford University Press; 1996:73, with permission.) C. During the manipulation and casting of a foot with MA, the subtalar joint is inverted to slight varus to help avoid inadvertent eversion of that joint. The latter could potentially convert MA to a skewfoot. A long-leg cast is recommended, as for clubfoot, but without the external rotation.D. The ankle is also slightly plantar flexed to further help avoid eversion stress on the subtalar joint.
Figure 5-41. Photos of a foot from an older child with residual MA. He has pain, tenderness, callus formation, and erythema (A) along the lateral midfoot and (B) medial to the head of the 1st MT and the hallux.
Figure 5-42. Idiopathic infant skewfoot. A. Forefoot adductus with a medial midfoot concavity immediately anterior to a convexity. The convexity is the head of the talus, and the concavity is the medially displaced navicular/midfoot. B. Medial midfoot crease at the junction of the medial concavity and convexity. C. Hindfoot valgus. D. The radiographic forefoot adductus and hindfoot valgus deformities (see Assessment Principle #18, Figure 3-23) match the clinical appearance of the foot. E. Lateral x-ray.
Figure 5-43. Skewfoot in a young child. A. The lateral x-ray looks essentially normal with a nearly straight talus–1st metatarsus angle and a normal calcaneal pitch. B. The AP x-ray clearly shows the skew deformities of hindfoot valgus/eversion and forefoot adductus.
3. Imaging
a. Standing AP and lateral of foot (see Assessment Principle #18, Figure 3-23, Chapter 3) (Figures 5-42 to 5-44)
b. There is no known association between skewfoot and hip dysplasia; so routine imaging of the hips is not indicated.
Figure 5-44. Adolescent skewfoot: valgus/eversion deformity of the hindfoot with a flat longitudinal arch and adduction of the forefoot on the midfoot. The medial cuneiform is trapezoid-shaped. A and B. Clinical photographs. C and D. Radiographs. (From Mosca VS. The Foot. In: Morrissy RT, Weinstein SL, eds. Lovell and Winter’s Pediatric Orthopaedics, 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2001; page 1166, Figure 29-13, with permission.)
4. Natural history
a. Unknown, at least in part due to the lack of a strict definition. It is not known how much forefoot adductus is necessary to reclassify a flatfoot as a skewfoot, or how much hindfoot valgus is necessary to reclassify a MA deformity as a skewfoot. Lack of a strict definition also prevents an estimation of prevalence.
b. Some young children develop pain, callosities, and shoe-fitting problems that are related to the forefoot adductus, with pain and tenderness along the lateral midfoot and/or medial to the head of the 1st MT and the hallux (Figures 5-41 and 5-45A).
c. Some older children and adolescents develop pain and callosities under the head of the plantar flexed talus or in the sinus tarsi that are related to the hindfoot valgus and contracture of the gastrocnemius or tendo-Achilles (similar to the signs and symptoms in flexible flatfoot with tight tendo-Achilles) (Figure 5-45B).
Figure 5-45. A. The forefoot adductus component of a skewfoot may contribute to the development of pain, tenderness, and callus formation along the lateral midfoot (black arrow) and/or medial to the head of the 1st MT (yellow arrow) and the hallux in young children. B. The hindfoot valgus deformity and contracture of the gastrocnemius or tendo-Achilles more commonly contribute to the development of pain, tenderness, and callus formation under the head of the plantar flexed talus (black oval) or in the sinus tarsi in older children and adolescents.
5. Nonoperative treatment
a. Serial casting of the forefoot adductus in young children. Casting of hindfoot valgus is never indicated or successful.
i. Best initiated between 6 and 12 months—after persistence of deformity is confirmed and before the forefoot becomes too stiff
ii. Cast the forefoot in the same manner as in a foot with MA with the ankle in slight plantar flexion and the subtalar joint in slight inversion (to avoid inadvertent further valgus stress on the already valgus subtalar joint) (see Figure 5-40).
b. Accommodative shoe wear
6. Operative indications
a. Failure of nonoperative treatment to relieve:
i. pain, callosities, and shoe-fitting problems in young children that are usually related to the forefoot adductus, with pain lateral to the base of the 5th MT and/or medial to the head of the 1st MT (Figure 5-45A)
ii. pain and callosities under the head of the plantar flexed talus or in the sinus tarsi in older children and adolescents that are related to the hindfoot valgus and contracture of the gastrocnemius or tendo-Achilles (similar to the signs and symptoms in flexible flatfoot with tight tendo-Achilles) (Figure 5-45B)
7. Operative treatment with reference to the surgical techniques section of the book for each individual procedure
a. Medial cuneiform opening wedge osteotomy (see Chapter 8) with or without a cuboid closing wedge osteotomy (see Chapter 8)—perform this in young children with pain lateral to the base of the 5th MT and/or medial to the head of the 1st MT. If the arch has not dropped yet, it will not—at least not right away. The TN joint and posterior tibialis tendon can be plicated for partial correction of the abduction at the TN joint.
b. Calcaneal lengthening osteotomy (see Chapter 8) and medial cuneiform opening wedge osteotomy (see Chapter 8) and gastrocnemius recession (see Chapter 7) or tendo-Achilles lengthening (see Chapter 7), as determined by the intraoperative Silfverskiold test (see Assessment Principle #12, Figure 3-13, Chapter 3)—perform this in older children and adolescents who have pain and callosities under the head of the plantar flexed talus or in the sinus tarsi (Figures 5-46 and 5-47)
Figure 5-46. A. Artist sketch of an AP x-ray of an adolescent skewfoot. B. Sketch of the lateral x-ray of the same foot. C. Sketch of the actual AP x-ray taken after a calcaneal lengthening osteotomy and a medial cuneiform opening wedge osteotomy. D. Sketch of the actual lateral x-ray taken after the operation. (From Mosca VS. Calcaneal lengthening for valgus deformity of the hindfoot. Results in children who had severe, symptomatic flatfoot and skewfoot. J Bone Joint Surg. 1995; 77(4):500–512.)